Method of crosslinking a carboxylated polymer using a triazine crosslinking activator

ABSTRACT

A method for crosslinking a carboxylated polymer using a triazine crosslinking activator.

FIELD OF THE INVENTION

The present invention relates to a method for crosslinking acarboxylated polymer using a triazine crosslinking activator.

BACKGROUND OF THE INVENTION

Methods for crosslinking cellulose are well known. In conventionalmethods for crosslinking cellulose, cellulose hydroxyl groups arereacted with a crosslinking agent having at least two functional groupsthat are reactive toward the cellulose hydroxyl groups. Traditionalcrosslinking agents include dialdehydes, such as glutaraldehyde, whichprovide acetal crosslinks, and polycarboxylic acid crosslinking agents,such as citric acid, that provide ester crosslinks.

Carboxylated celluloses may be crosslinked either through the cellulosehydroxyl groups, or by using a crosslinking agent that is reactivetoward the cellulose carboxylic acid groups. Crosslinking agents usefulin crosslinking carboxylated cellulose through its carboxyl groupsinclude crosslinking agents having two or more hydroxyl groups, so as toprovide diester crosslinks, and crosslinking agents that include two ormore amino groups, so as to provide diamide crosslinks. Although diamidecrosslinks are more stable than diester crosslinks, amide formation isoftentimes more difficult than ester formation.

Typically, amides are prepared by coupling an amine with an acidchloride derived from a carboxylic acid. Although acid chlorides arehighly reactive, the preparation of an acid chloride from a carboxylicacid in large scale poses significant difficulties due to the reagentsnecessary for making the acid chloride. Most importantly, because acidchlorides are sensitive to water, and because cellulose modification isoften carried out in aqueous medium, acid chlorides are not suitable forthe formation of cellulose amides. Amidation methods using acidanhydrides as reactive intermediates are also known. However, like acidchlorides, acid anhydrides are also difficult to prepare in aqueousmedia.

The disadvantages of the use of acid chlorides and anhydrides inamidation methods has caused the development of alternative syntheticprocesses for amidation. One approach involves the generation of anactivated carboxylic acid intermediate that is then treated with anamine in situ to form an amide product.

Recently, a process for triazine-promoted amidation of carboxylic acidshas been developed. In the method, amides are prepared from carboxylicacids using a triazine reagent as a promoter. In the method,2,4,6-trichloro-1,3,5-triazine (also known as cyanuric chloride) istreated with three equivalents of a carboxylic acid in the presence ofbase in a polar organic solvent to provide the activated carboxylic acidderivative. To the activated carboxylic acid derivative is added anamine in an amount that is a slight excess relative to the carboxylicacid. The product of the reaction is the corresponding amide that isreadily separated from the cyanuric acid by-product.

Despite the advances in the development of amidation processes, a needexists for the formation of cellulose amides in aqueous environmentstypically used for cellulose modification. The present invention seeksto fulfill this need and provides further related advantages. Thepresent invention provides a method for the amidation of cellulosepromoted by triazine reagents. In the method, a cellulose carboxylicacid is converted to a cellulose amide by reaction of the carboxylicacid group with a triazine reagent to provide an activated carboxylicacid derivative in situ that is then reacted with an amine to provide acellulose amide. In the method of the invention, the modification of thecellulose carboxylic acid is carried out in an aqueous environment.

SUMMARY OF THE INVENTION

The invention provides a method for crosslinking a carboxylated polymer.In the method, a carboxylated polymer having a plurality of carboxylgroups is treated with a triazine crosslinking activator to provide anactivated carboxylated polymer. The activated carboxylated polymer isthen reacted with an amine compound (e.g., a diamine or a polyamine)having at least one amino group reactive toward an activated carboxylgroup of the activated carboxylated polymer to form a plurality of amidebonds. The plurality of amide bonds results in polymer crosslinkingthereby providing a crosslinked carboxylated polymer. In one embodiment,the method provides a diamide crosslinked carboxylated polymer. Inanother embodiment, the method provides an ionic crosslinkedcarboxylated polymer.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of a diamide crosslink and an ioniccrosslink formed in accordance with the present invention; and

FIG. 2 is a schematic illustration of a device for measuring AbsorbencyUnder Load (AUL) values.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In one aspect, the present invention provides a crosslinked carboxylatedpolymer and a method for crosslinking a carboxylated polymer.

In the method, a carboxylated polymer having a plurality of carboxylgroups is treated with a triazine crosslinking activator to provide anactivated carboxylated polymer. The activated carboxylated polymer isthen reacted with an amine compound (e.g., a diamine or a polyamine)having at least one amino group reactive toward an activated carboxylgroup of the activated carboxylated polymer to form a plurality of amidebonds. The plurality of amide bonds results in polymer crosslinkingthereby providing a crosslinked carboxylated polymer.

As used herein, the term “carboxylated polymer” refers to a polymerhaving a plurality of carboxyl groups (i.e., carboxylic acid groups orcarboxylate salt groups). In one embodiment, the carboxylated polymer isa carboxyalkyl cellulose, such as a carboxymethyl cellulose orcarboxyethyl cellulose. In one embodiment, the carboxylated polymer is acarboxy cellulose in which the C6 hydroxyl glucose group has beenoxidized to a carboxylic acid group (i.e., a glucuronic acid). Othercarboxylated polymers include polysaccharides that are natural,synthetic, or semi-synthetic in origin. Exemplary polysaccharidesinclude hyaluronic acids, carboxymethyldextran, carboxyalkyl starches,alginic acids, carboxymethyl or butyl glucans or chitosans. In oneembodiment, the carboxylated polymer is a polyacrylic acid. In oneembodiment, the carboxylated polymer is a polymaleic acid. In oneembodiment, the carboxylated polymer is a polyaspartic acid. In oneembodiment, the carboxylated polymer is a copolymer of acrylic acid andacrylamide (i.e., a poly(acrylamide-co-acrylic acid)). In oneembodiment, the carboxylated polymer is an at least partially hydrolyzedpolyacrylamide polymer

The term “activated carboxylated polymer” refers to a carboxylatedpolymer in which one or more of the plurality of the carboxyl groups areactivated for reaction with an amine to provide an amide by treatmentwith a triazine crosslinking activator. The crosslinking activator is ahalogenated triazine. In one embodiment, the crosslinking activator is2,4,6-trichloro-1,3,5-triazine (also known as cyanuric chloride). In oneembodiment, the crosslinking activator is2-chloro-4,6-dimethoxy-1,3,5-triazine.

In one embodiment of the method, the carboxylated polymer is treatedwith the triazine crosslinking activator in an aqueous solvent.

In the method, the activated carboxylated polymer is reacted with anamine compound (e.g., a diamine or a polyamine). As used herein, theterm “polyamine” refers to an amine having three or more amino groups.In one embodiment, the diamine or polyamine is a water-soluble diamineor water-soluble polyamine. The diamine or polyamine includes either aprimary amino group or a secondary amino group. In one embodiment, thediamine or polyamine includes two primary amino groups. In oneembodiment, the diamine or polyamine includes a primary amino group anda secondary amino group. In one embodiment, the diamine or polyamineincludes two secondary amino groups. In one embodiment, the diamine orpolyamine is a poly(oxyalkylene)diamine.

To effect amide bond formation with a carboxylated polymer, theamine-containing crosslinking agents useful in the methods of theinvention include at least one primary amino group. To effect diamidecrosslink formation, the amine-containing crosslinking agent includestwo primary amino groups. In one embodiment, the crosslinking agent is adiamine having two primary amino groups. In another embodiment, thecrosslinking agent is a polyamine (i.e., an amine that includes three ormore amino groups) having at least two primary amino groups. To effectionic crosslink formation, the amine-containing crosslinking agentincludes at least one primary amino group or reactive secondary aminogroup for amide bond formation and a secondary, tertiary, or quaternaryamino group for ionic association with a carboxylated polymer'scarboxylic acid group.

In one embodiment, the crosslinking agent is a polyether diamine.Suitable polyether diamines include polyalkylene diamines, for example,polyalkylene diamines commercially available from Huntsman Corp.,Houston, Tex., under the designation JEFFAMINE. Representativepolyalkylene diamines useful in the crosslinking methods of theinvention are described and depicted below. In one embodiment, thecrosslinking agent is a polyether polyamine, such as a polyalkylenepolyamine commercially available from Huntsman Corp., Houston, Tex.,under the designation JEFFAMINE. In certain embodiments, thepolyoxyalkylene diamines include two or more primary amine groups.

In one embodiment, the crosslinking agent is a polyalkylene polyamine.Suitable polyalkylene polyamines include, for example,diethylenetriamine, triethylenetetraamine, and tetraethylenepentaamine.

Representative primary diamines and polyamines (e.g., tri-, tetra-, andpentamines) useful in crosslinking methods of the invention includeJEFFAMINE D-230 (molecular weight 230), JEFFAMINE D-400 (molecularweight 400), and JEFFAMINE D-2000 (molecular weight 2000) depicted belowhaving formula (1), where x is an integer sufficient to provide theindicated molecular weight (i.e., x=2-3, 5-6, and about 33,respectively); JEFFAMINE XTJ-510 (D-4000) (molecular weight 4000),JEFFAMINE XTJ-50 (ED-600) (molecular weight 600) (y=2, and x+z=2),JEFFAMINE XTJ-501 (ED-900) (molecular weight 900), and JEFFAMINE XTJ-502(ED-2003) (molecular weight 2000) (y=39, and x+Z=6) depicted belowhaving formula (2), where x, y, and z are integers sufficient to providethe indicated molecular weight; JEFFAMINE XTJ-504 (EDR-148) (molecularweight 148) depicted below having formula (3); JEFFAMINE HK-511(molecular weight 225) depicted below as having formula (4); andethylenediamine, diethylenetriaamine, triethylenetetraamine, andtetraethylenepentaamine, also depicted below.NH₂CH(CH₃)CH₂—[OCH₂CH(CH₃)]_(x)—NH₂  (1)NH₂CH(CH₃)CH₂[OCH(CH₃)CH₂]_(x)—[OCH₂CH₂]_(y)—[OCH₂CH(CH₃)]_(z)—NH₂  (2)NH₂(CH₂CH₂O)₂—CH₂CH₂NH₂  (3)NH₂CH(CH₃)CH₂—(OCH₂CH₂)₂—OCH₂CH(CH₃)NH₂  (4)NH₂CH₂CH₂NH₂NH₂CH₂CH₂NHCH₂CH₂NH₂NH₂CH₂CH₂NHCH₂CH₂NHCH₂CH₂NH₂NH₂(CH₂CH₂NH)₃—CH₂CH₂NH₂

Other representative primary polyamines (i.e., triamines) useful incrosslinking methods of the invention include JEFFAMINE T-403 (molecularweight 440) depicted below having formula (5), where x, y, and z areintegers sufficient to provide the indicated molecular weight; andJEFFAMINE T-5000 (molecular weight 5000) and JEFFAMINE XTJ-509 (T-3000)(molecular weight 3000) depicted below having formula (6), where x, y,and z are integers sufficient to provide the indicated molecular weight.

In one embodiment, the crosslinking method provides a crosslinkedcarboxylated

polymer that includes one or more diamide crosslinks. As used herein,the term “diamide crosslink” refers to a crosslink that includes twoamide bonds. A diamide crosslink is formed by reaction of a firstactivated carboxyl group with a diamine or polyamine to provide a firstamide, the resulting amide having a second amino group reactive toward asecond activated carboxyl group, and subsequent reaction of a secondactivated carboxyl group with the second amino group to provide a secondamide.

A diamide crosslink formed in accordance with the present invention isillustrated schematically in FIG. 1. FIG. 1 illustrates anintermolecular diamide crosslink. It will be appreciated that thediamide crosslink formed in accordance with the invention can also be anintramolecular diamide crosslink (i.e., a diamide crosslink within onecarboxylated polymer chain).

The preparation of a representative diamide crosslinked carboxymethylcellulose polymer is described in Example 1. The absorbent properties(i.e., free swell capacity, centrifuge capacity, and absorbency underload (AUL)) of representative diamide crosslinked carboxymethylcellulose polymers are summarized in Table 2 below.

As noted above, in the method, the activated carboxylated polymer isreacted with a diamine or polyamine that includes either a primary aminogroup or a secondary amino group. In one embodiment, in addition to theprimary or secondary amino group, the diamine or polyamine also includeseither a tertiary amino group or a quaternary amino group. In oneembodiment, the diamine or polyamine includes a primary amino group andat least one of a tertiary amino group or a quaternary amino group. Inone embodiment, the diamine or polyamine includes a secondary aminogroup and at least one of a tertiary amino group or a quaternary aminogroup. In one embodiment, the diamine is 3-(dimethylamino)propylamine.

Representative crosslinking agents including secondary and tertiaryamine groups useful in crosslinking methods of the invention includedimethylaminopropylamine (DMAPA), aminopropylmorpholine,N-aminoethylpiperazine, aminopropylmonomethylethanolamine,diethylenetriaamine, triethylenetetraamine, and tetraethylenepentaamine.Dimethylaminopropylamine (DMAPA), aminopropylmorpholine,N-aminoethylpiperazine, aminopropylmonomethylethanolamine are depictedbelow.

In one embodiment, the crosslinking method provides a crosslinkedcarboxylated polymer that includes one or more ionic crosslinks. As usedherein, the term “ionic crosslink” refers to a crosslink that includesan amide bond and an ionic bond or association between an amino groupand a carboxyl group. An ionic crosslink is formed by reaction of afirst activated carboxyl group with a diamine or polyamine to provide afirst amide, the resulting amide having a second amino group that isionically reactive or associative toward a second carboxyl group.

An ionic crosslink formed in accordance with the present invention isillustrated schematically in FIG. 1. FIG. 1 illustrates anintermolecular ionic crosslink. It will be appreciated that the ioniccrosslink formed in accordance with the invention can also be anintramolecular ionic crosslink (i.e., an ionic crosslink within onecarboxylated polymer chain).

The preparation of a representative ionic crosslinked carboxymethylcellulose polymer is described in Example 2. The absorbent properties(i.e., free swell capacity, centrifuge capacity, and absorbency underload (AUL)) of representative ionic crosslinked carboxymethyl cellulosepolymers are summarized in Table 1. Methods for measuring free swellcapacity and centrifuge capacity are described in Example 7. A methodfor measuring absorbency under load (AUL) is described in Example 8.

TABLE 1 Representative Ionic Crosslinked Carboxymethyl CellulosePolymers: Absorbent Properties. Carboxymethyl Cyanuric ChlorideDimethyamino Yield Free Swell Centrifuge AUL Cellulose (wt %)propylamine (wt %) (%) (g/g) (g/g) (g/g) CMC 9H4F 2.0 3.2 89.15 38.3625.84 19.27 CMC 9H4F 5.4 9.0 98.36 41.51 29.68 16.46 CMC 9H4F 1.0 1.678.66 29.25 16.00 19.12 CMC 9H4F 2.8 4.8 98.19 24.08 14.08 17.11 CMC(Weyerhaeuser) 2.0 3.2 56.47 17.24 7.89 11.00 CMC (Weyerhaeuser) 2.0 3.267.89 20.89 10.17 13.79

In one embodiment, the crosslinked carboxylated polymer made by themethod of the invention includes one or more diamide crosslinks and oneor more ionic crosslinks.

The amount of second polymer used in the method can range from about 1to about 99 percent by weight based on the weight of the firstcarboxylated polymer.

The crosslinked polymers of the invention have a free swell capacity offrom about 10 to about 80 g/g, a centrifuge capacity of from about 10 toabout 60 g/g, and absorbency under load (AUL) of from about 5 to about35 g/g.

In another aspect, the invention provides a crosslinked carboxylatedpolymer. The crosslinked carboxylated polymer includes a plurality ofcarboxyl groups that are treated with an amount of a diamine orpolyamine having at least one amino group reactive toward a carboxylgroup of the carboxylated polymer to form an amide bond and at least oneamino group that is reactive toward a carboxyl group of the carboxylatedpolymer to form an ionic bond.

In one embodiment, the crosslinked carboxylated polymer comprises acarboxylated polymer having plurality of crosslinks, each of theplurality of crosslinks comprising a first bond and a second bond. Inthe crosslinked polymer, the first bond is an amide bond formed betweena carboxyl group of the carboxylated polymer and a first amino group ofa crosslinking agent, and the second bond is an ionic bond formedbetween a carboxyl group of the carboxylated polymer and a second aminogroup of the crosslinking agent.

In another aspect, the invention provides a method for crosslinking amixture of first carboxylated polymers and second carboxylated polymers.In the method, a mixture of a first carboxylated polymer having aplurality of carboxyl groups and a second carboxylated polymer having aplurality of carboxyl groups is treated with a triazine crosslinkingactivator to provide a mixture of first and second activatedcarboxylated polymers, which are subsequently reacted with either adiamine or polyamine having two amino groups reactive toward activatedcarboxyl groups, or a diamine or polyamine having one amino groupreactive toward activated carboxyl groups and one amino group that isnot reactive toward activated carboxyl groups.

In one embodiment, the mixture of activated carboxylated polymers isreacted with a diamine or polyamine having two amino groups (i.e., twoprimary amino groups, two secondary amino groups, or a primary aminogroup and a secondary amino group) reactive toward activated carboxylgroups of the first and second activated carboxylated polymers to form aplurality of diamide crosslinks to provide a crosslinked carboxylatedpolymer.

The preparations of representative diamide crosslinked carboxylatedpolymer products (i.e., diamide crosslinked mixtures of a carboxymethylcellulose polymer and a second carboxylated polymer) are described inExamples 3 and 4. The absorbent properties (i.e., free swell capacity,centrifuge capacity, and absorbency under load (AUL)) of representativediamide crosslinked mixtures of a carboxymethyl cellulose polymer and asecond carboxylated polymer are summarized in Table 2.

TABLE 2 Representative Diamide Crosslinked Carboxymethyl CellulosePolymers: Absorbent Properties. Free Second Polymer Cyanuric ChlorideDiamine Yield Swell Centrifuge AUL (wt %) (wt %) (wt %) (%) (g/g) (g/g)(g/g) Polyacrylic Acid (10%) 1.8 JEFFAMINE 400 (6.1) 109.94 41.51 25.9115.52 Polyacrylic Acid (10%) 3.5 JEFFAMINE 400 (11.5) 104.77 33.75 20.8714.97 Polyacrylic Acid (10%) 6.3 JEFFAMINE 400 (20) 97.14 36.25 23.4615.87 Polyacrylic Acid (10%) 8.6 JEFFAMINE 400 (28) 87.48 29.43 20.6413.92 Polyacrylic Acid (10%) 10.5 JEFFAMINE 400 (34.2) 83.68 30.58 21.289.75 — 5.0 JEFFAMINE 400 (16.3) 84.85 31.34 20.05 16.44 — 5.0 JEFFAMINE230 (10.0) 92.17 34.74 21.86 15.12 Poly(AmCoAc) (10%) 2.0 JEFFAMINE 400(7.2) 104.13 40.36 22.07 16.20 Poly(AmCoAc) (9.5%) 3.9 JEFFAMINE 400(12.6) 100.19 34.53 22.01 19.93 Poly(AmCoAc) (8.8%) 5.4 JEFFAMINE 400(19.4) 94.79 30.17 19.95 18.48 Poly(AmCoAc) (8.5%) 6.9 JEFFAMINE 400(22.5) 95.68 20.65 19.27 17.18

In another embodiment, the mixture of activated carboxylated polymers isreacted with a diamine or polyamine having one amino group that isreactive toward the activated carboxyl groups of the first and secondactivated carboxylated polymers to form a plurality of amide bonds and asecond amino group (i.e., a tertiary amino group or a quaternary aminogroup) that is not covalently reactive toward the activated carboxylgroups of the first and second activated carboxylated polymers. Theresulting polymer is a crosslinked carboxylated polymer having aplurality of amide bonds and a plurality of ionic bonds between thenon-covalently reactive amino group (i.e., tertiary or quaternary aminogroups) and carboxyl groups, thereby effectively crosslinking thepolymers to provide a crosslinked carboxylated polymer. In certaincases, secondary amino groups may also be non-covalently reactive towardactivated carboxyl groups and therefore useful for forming ioniccrosslinks.

The preparations of representative ionic crosslinked carboxylatedpolymer products (i.e., ionic crosslinked mixtures of a carboxymethylcellulose polymer and a second carboxylated polymer) are described inExamples 5 and 6. The absorbent properties (i.e., free swell capacity,centrifuge capacity, and absorbency under load (AUL)) of representativeionic crosslinked mixtures of a carboxymethyl cellulose polymer and asecond carboxylated polymer are summarized in Table 3.

TABLE 3 Representative Ionic Crosslinked Carboxymethyl CellulosePolymers: Absorbent Properties. Second Polymer Cyanuric ChlorideDimethylamino Yield Free Swell Centrifuge AUL (wt %) (wt %) propylamine(wt %) (%) (g/g) (g/g) (g/g) Polyacrylic Acid (10%) 0.9 1.3 111.5 59.2043.00 21.07 Polyacrylic Acid (10%) 1.7 2.7 108.06 67.30 50.82 17.07Polyacrylic Acid (10%) 2.5 4.2 108.36 66.37 45.42 14.02 Polyacrylic Acid(10%) 4.7 7.8 108.23 61.85 44.99 15.81 Poly(AcAmCoAc) (10%) 0.9 1.3107.96 54.09 31.26 13.95 Poly(AcAmCoAc) (10%) 1.7 2.7 111.98 45.93 24.9314.21 Poly(AcAmCoAc) (10%) 2.5 4.2 115.78 48.44 23.43 13.10Poly(AcAmCoAc) (10%) 4.7 7.8 111.52 41.28 19.95 13.30

In the above tables, “Poly(AcAmCoAc)” refers topoly(acrylamide-co-acrylic acid).

In one embodiment of the method, the mixture of the first and secondcarboxylated polymers are treated with a triazine crosslinking activatorin an aqueous solvent.

To further illustrate various embodiments of the methods of theinvention, the following representative exemplary methods are provided.

As noted above, in one embodiment, the present method for crosslinkingcarboxylic acid-containing polymers (carboxylated polymers) providescrosslinked carboxylic acid polymers that include diamide (or polyamide)crosslinks. In the method, carboxylate salts of carboxylated polymers inaqueous medium are activated with a triazine crosslinking activator(e.g., cyanuric chloride) and crosslinked with a diamine or a polyamine(that includes primary and/or secondary amino groups) to form diamide orpolyamide crosslinks.

If a single carboxylated polymer in aqueous solution is crosslinked withcyanuric chloride activation and a diamine or a polyamine, the amidebonds may bridge two or more carboxylated polymer chains (i.e.,intermolecular crosslinking). The crosslinker may also form amide bondswithin a single polymer chain having multiple carboxylic acid groups(i.e., intramolecular crosslinking).

If a mixture of polycarboxylated polymers in aqueous solution iscrosslinked with cyanuric chloride activation and a diamine or apolyamine, the amide bonds may bridge two or more carboxylated polymerchains of the same polymer or different polymers (i.e., intermolecularcrosslinking). The crosslinker may also form amide bonds with a singlepolymer chain of one type of polymer in the mixture having multiplecarboxylic acid groups (i.e., intramolecular crosslinking).

In another embodiment, the present method for crosslinking carboxylicacid-containing polymers provides crosslinked carboxylic acid polymersthat include ionic crosslinks. In the method, carboxylate salts ofcarboxylated polymers in aqueous medium are activated with a triazinecrosslinking activator (e.g., cyanuric chloride) and crosslinked with adiamine or a polyamine (that includes at least one or more primaryand/or secondary amino groups and at least one or more tertiary orquaternary amino groups) to form ionic crosslinks.

If a single carboxylated polymer in aqueous solution is crosslinked withcyanuric chloride activation and a diamine, the amide bond is formed byreaction of the primary amino group with carboxylic acid group of acarboxylated polymer. The unreacted quaternary amino, tertiary amino, orless reactive secondary amino terminal may form an ionic bond orassociation with another carboxylic acid group of the same polymer chain(i.e., intramolecular crosslinking) or an ionic bond or association witha carboxylic acid group of another polymer chain of the same polymer(i.e., intermolecular crosslinking).

If a single carboxylated polymer in aqueous solution is crosslinked withcyanuric chloride activation and a polyamine, an amide bond is formed byreaction of the primary amino group with carboxylic acid group of acarboxylated polymer. If more than one primary amino group is present inthe polyamine, then crosslinking described above for diamines (orpolyamines) applies. If only one primary amino group is present in thepolyamine, the unreacted tertiary amino or less reactive secondary aminoterminals may form ionic bonds or associations with other carboxylicacid groups of the same polymer chain (i.e., intramolecularcrosslinking) or ionic bonds or associations with carboxylic acid groupsof another polymer chain of the same polymer (i.e., intermolecularcrosslinking).

If a mixture of carboxylated polymers in aqueous solution is crosslinkedwith cyanuric chloride activation and a diamine, an amide bond is formedby reaction of the primary amino group with carboxylic acid group of acarboxylated polymer. The unreacted quaternary amino, tertiary amino, orless reactive secondary amino terminal may form an ionic bond orassociation with another carboxylic acid group of the same polymer chain(i.e., intramolecular crosslinking) or an ionic bond or association witha carboxylic acid group of another polymer chain of the same polymer(i.e., intramolecular crosslinking) or a different polymer (i.e.,intermolecular crosslinking).

If a mixture of carboxylated polymers in aqueous solution is crosslinkedwith cyanuric chloride activation and a polyamine, an amide bond isformed by reaction of the primary amino group with carboxylic acid groupof a carboxylated polymer. If more than one primary amino group ispresent in the polyamine, then crosslinking described for diamines (orpolyamines) applies. If only one primary amino group is present in thepolyamine, the unreacted quaternary amino, tertiary amino, or lessreactive secondary amino terminals may form ionic bonds or associationswith other carboxylic acid groups of the same polymer chain (i.e.,intramolecular crosslinking), or ionic bonds or associations withcarboxylic acid groups of another polymer chain of the same polymer(i.e., intramolecular crosslinking) or different polymer (i.e.,intermolecular crosslinking).

In another aspect, the invention provides a composition comprising afirst carboxylated polymer having a plurality of carboxyl groups and asecond carboxylated polymer having a plurality of carboxyl groupstreated with an amount of an amine compound (e.g., a diamine or apolyamine) having at least two amino groups reactive toward the carboxylgroups to form a plurality of amide bonds.

In one embodiment, the composition comprises a plurality of firstcarboxylated polymers, a plurality of second carboxylated polymers, anda plurality of crosslinks, each of the plurality of crosslinkscomprising a first bond and a second bond. The first bond is an amidebond formed between a carboxyl group of the first or second carboxylatedpolymers and a first amino group of a crosslinking agent (e.g., adiamine or a polyamine), and the second bond is an amide bond formedbetween a carboxyl group of the first or second carboxylated polymersand a second amino group of the crosslinking agent.

In one embodiment, the composition comprises a plurality of firstcarboxylated polymers, a plurality of second carboxylated polymers, anda plurality of crosslinks, each of the plurality of crosslinkscomprising a first bond and a second bond. The first bond is an amidebond formed between a carboxyl group of the first or second carboxylatedpolymers and a first amino group of a crosslinking agent (e.g., adiamine or a polyamine), and the second bond is an ionic bond formedbetween a carboxyl group of the first or second carboxylated polymersand a second amino group of the crosslinking agent.

The present invention provides a method for the amidation of cellulosepromoted by triazine reagents. In the method, a cellulose carboxylicacid is converted to a cellulose amide by reaction of the carboxylicacid group with a triazine reagent to provide an activated carboxylicacid derivative in situ that is then reacted with an amine to provide acellulose amide. In the method of the invention, the modification of thecellulose carboxylic acid is carried out in an aqueous environment.

The following examples are provided for the purpose of illustrating, notlimiting, the invention.

EXAMPLES Example 1 The Preparation and Absorbent Properties of aRepresentative Diamide Crosslinked Carboxylated Polymer: CrosslinkedCarboxymethyl Cellulose

In this example, the preparation and absorbent properties of arepresentative diamide crosslinked carboxylated polymer are described.Carboxymethyl cellulose activated by cyanuric chloride was crosslinkedwith a poly(oxyalkylene)diamine as described below.

Carboxymethyl cellulose; sodium salt (Aqualon 9H4F), 10.0 g, wasdissolved in 1000 mL de-ionized water with efficient stirring to give ahomogeneous solution. The carboxyl activating agent, cyanuric chloride(Sigma-Aldrich), 0.60 g, was added as a fine powder and mixed. Themixture was allowed to stand at 25° C. for 3 hours. A primary diamine,JEFFAMINE D-230, MW=230 (Huntsman), 1.12 g, was added and mixed. Themixture was allowed to stand for 10 hours at 25° C. The crosslinkedpolymer was then precipitated with 4000 mL technical acetone. Theprecipitated polymer was filtered. Another 500 mL acetone was added tothe precipitated polymer and stirred to remove most of the water fromthe polymer. The regenerated polymer was filtered and air dried at 25°C. to give the polymer product. A sample of the polymer product wasground to particle size of 300-800 μm and tested for free swell (34.7g/g), centrifuge capacity (21.8 g/g), and absorbance under load (15.1g/g) in 1% saline solution.

Example 2 The Preparation and Absorbent Properties of a RepresentativeIonic Crosslinked Carboxylated Polymer: Crosslinked CarboxymethylCellulose

In this example, the preparation and absorbent properties of arepresentative ionic crosslinked carboxylated polymer are described.Carboxymethyl cellulose activated by cyanuric chloride was crosslinkedwith dimethylaminopropylamine as described below.

Carboxymethyl cellulose, sodium salt (Aqualon 9H4F), 10.0 g, wasdissolved in 1000 mL de-ionized water with efficient stirring to give ahomogeneous solution. The carboxyl activating agent, cyanuric chloride(Sigma-Aldrich), 0.20 g, was then added and mixed. The mixture wasallowed to stand for 3 hours at 25° C. Dimethylaminopropylamine (DMAPA)(Sigma-Aldrich), 0.33 g, was added and mixed. The mixture was allowed tostand for 10 hours at 25° C. The crosslinked polymer was thenprecipitated with 4000 mL technical acetone. The precipitated polymerwas filtered. Another 500 mL acetone was added to the precipitatedpolymer and stirred to remove most of the water from the polymer. Theregenerated polymer was filtered and air dried at 25° C. to give thepolymer product. A sample of the polymer product was ground to particlesize of 300-800 μm and tested for free swell (38.4 g/g), centrifugecapacity (25.8 g/g), and absorbance under load (19.2 g/g) in 1% salinesolution.

Example 3 The Preparation and Absorbent Properties of a RepresentativeDiamide Crosslinked Carboxylated Polymer: Crosslinked CarboxymethylCellulose/Polyacrylic Acid

In this example, the preparation and absorbent properties of arepresentative diamide crosslinked carboxylated polymer are described. Amixture of carboxymethyl cellulose and polyacrylic acid activated bycyanuric chloride was crosslinked with a poly(oxyalkylene)diamine asdescribed below.

Carboxymethyl cellulose, sodium form (Aqualon 9H4F), 4.5 g, andpolyacrylic acid, MW=4,000,000 (Sigma-Aldrich), 0.5 g, was completelydissolved in 500 mL de-ionized water and mixed to give a homogeneouspolymer mixture. The pH was adjusted to 7.0 with 10% aqueous sodiumcarbonate solution. The carboxyl activating agent, cyanuric chloride(Sigma-Aldrich), 0.20 g, was added as a fine powder and mixed well. Themixture was allowed to stand at 25° C. for 3 hours. A primary diamine,JEFFAMINE 400, MW=400 (Huntsman), 0.65 g, was added and mixed. Themixture was allowed to stand for 10 hours at 25° C. The crosslinkedpolymer mixture was precipitated with 2.0 L technical acetone. Theprecipitate was separated and stirred in another 500 mL acetone tocompletely remove water. The regenerated polymer was filtered and airdried to give the polymer product.

The polymer product was ground to particle size 300-800 μm and testedfor free swell (33.7 g/g), centrifuge capacity (20.8 g/g), andabsorbance under load (14.9 g/g) in 1% saline solution.

Example 4 The Preparation and Absorbent Properties of a RepresentativeDiamide Crosslinked Carboxylated Polymer: Crosslinked CarboxymethylCellulose/Poly(Acrylamide-co-Acrylic Acid)

In this example, the preparation and absorbent properties of arepresentative diamide crosslinked carboxylated polymer are described. Amixture of carboxymethyl cellulose and poly(acrylamide-co-acrylic acid)activated by cyanuric chloride was crosslinked with apoly(oxyalkylene)diamine as described below.

Carboxymethyl cellulose, sodium salt, (Aqualon), 4.0 g. andpoly(acrylamide-co-acrylic acid), MW=5,000,000 (Sigma-Aldrich), 0.46 g(0.61 g with 15% water and 10% sodium sulfate), was stirred in 400 mLde-ionized water to give a homogeneous solution. The carboxyl activatingagent, cyanuric chloride (Sigma-Aldrich), 0.20 g, was added as a finepowder and mixed. The mixture was allowed to stand at 25° C. for 3hours. A primary diamine, JEFFAMINE D-400, MW=400 (Huntsman), 0.65 g,was added and mixed. The mixture was allowed to stand for 10 hours at25° C. The crosslinked polymer was then precipitated with 1600 mLtechnical acetone. The precipitated product was filtered. Theregenerated product was placed in another 500 mL acetone and stirred toremove most of the water from the fiber. The polymer product wasfiltered and air dried at 25° C. to give polymer product. A sample ofpolymer product was ground to particle size 300-800 μm and tested forfree swell (34.5 g/g), centrifuge capacity (22.0 g/g) and, absorbanceunder load (19.9 g/g) in 1% saline solution.

Example 5 The Preparation and Absorbent Properties of a RepresentativeIonic Crosslinked Carboxylated Polymer: Crosslinked CarboxymethylCellulose/Polyacrylic Acid

In this example, the preparation and absorbent properties of arepresentative ionic crosslinked carboxylated polymer are described. Amixture of carboxymethyl cellulose and polyacrylic acid activated bycyanuric chloride was crosslinked with dimethylaminopropylamine asdescribed below.

Carboxymethyl cellulose, sodium salt (Aqualon), 4.0 g, and polyacrylicacid, MW=4,000,000 (Sigma-Aldrich), 0.46 g, was dissolved in 200 mLde-ionized water with efficient mixing to give a homogeneous solution.The pH was adjusted to 7.0 with 10% aqueous sodium carbonate solution.The carboxyl activating agent, cyanuric chloride (Sigma-Aldrich), 0.04g, was added as a fine powder and mixed. The mixture was allowed tostand for 3 hours at 25° C. Dimethylaminopropylamine (DMAPA)(Sigma-Aldrich), 0.06 g, was added and mixed. The mixture was allowed tostand for 10 hours at 25° C. The crosslinked polymer was thenprecipitated with 1600 mL technical acetone. The precipitated polymerwas filtered. Another 500 mL acetone was added to the precipitatedpolymer and stirred to remove most of the water from the fiber. Theregenerated polymer was filtered and air dried at 25° C. to give thepolymer product. A sample of the polymer product was ground to particlesize of 300-800 μm and tested for free swell (59.2 g/g), centrifugecapacity (43.0 g/g), and absorbance under load (21.0 g/g) in 1% salinesolution.

Example 6 The Preparation and Absorbent Properties of a RepresentativeIonic Crosslinked Carboxylated Polymer: Crosslinked CarboxymethylCellulose/Poly(Acrylamide-co-Acrylic Acid)

In this example, the preparation and absorbent properties of arepresentative ionic crosslinked carboxylated polymer are described. Amixture of carboxymethyl cellulose and poly(acrylamide-co-acrylic acid)activated by cyanuric chloride was crosslinked withdimethylaminopropylamine as described below.

Carboxymethyl cellulose, sodium salt (Aqualon), 4.0 g, andpoly(acrylamide-co-acrylic acid), MW=5,000,000 (Sigma-Aldrich), 0.46 g(0.61 g with 15% water and 10% sodium sulfate) was dissolved in 200 mLde-ionized water to give a homogeneous solution. The carboxyl activatingagent, cyanuric chloride (Sigma-Aldrich), 0.04 g, was added as a finepowder and mixed well. The mixture was allowed to stand for 3 hours at25° C. Dimethylaminopropylamine (DMAPA) (Sigma-Aldrich), 0.06 g, wasadded and mixed. The mixture was allowed to stand for 10 hours at 25° C.The crosslinked polymer was then precipitated with 1600 mL technicalacetone. The precipitated polymer was filtered. Another 500 mL acetonewas added and stirred to remove most of the water from the polymer. Thepolymer was filtered and air dried at 25° C. to give the polymerproduct. A sample of the polymer product was ground to particle size of300-800 μm and tested for free swell (54.0 g/g), centrifuge capacity(31.2 g/g) and absorbance under load (13.9 g/g) in 1% saline solution.

Example 7 Method for Determining Free Swell Capacity and CentrifugeCapacity

In this example, a method for determining free swell capacity (g/g) andcentrifuge capacity (g/g) is described.

The materials, procedure, and calculations to determine free swellcapacity (g/g) and centrifuge capacity (g/g) were as follows.

Test Materials:

Japanese pre-made empty tea bags (available from Drugstore.com, INPURSUIT OF TEA polyester tea bags 93 mm×70 mm with fold-over flap.(http:www.mesh.ne.jp/tokiwa/).

Balance (4 decimal place accuracy, 0.0001 g for air-dried superabsorbentpolymer (AD SAP) and tea bag weights).

Timer.

1% Saline.

Drip rack with clips (NLM 211)

Lab centrifuge (NLM 211, Spin-X spin extractor, model 776S, 3,300 RPM,120v).

Test Procedure:

1. Determine solids content of AD SAP.

2. Pre-weigh tea bags to nearest 0.0001 g and record.

3. Accurately weigh 0.2025 g+/−0.0025 g of test material (SAP), recordand place into pre-weighed tea bag (air-dried (AD) bag weight). (AD SAPweight+AD bag weight=total dry weight).

4. Fold tea bag edge over closing bag.

5. Fill a container (at least 3 inches deep) with at least 2 inches with1% saline.

6. Hold tea bag (with test sample) flat and shake to distribute testmaterial evenly through bag.

7. Lay tea bag onto surface of saline and start timer.

8. Soak bags for specified time (e.g., 30 minutes).

9. Remove tea bags carefully, being careful not to spill any contentsfrom bags, hang from a clip on drip rack for 3 minutes.

10. Carefully remove each bag, weigh, and record (drip weight).

11. Place tea bags onto centrifuge walls, being careful not to let themtouch and careful to balance evenly around wall.

12. Lock down lid and start timer. Spin for 75 seconds.

13. Unlock lid and remove bags. Weigh each bag and record weight(centrifuge weight).

Calculations:

The tea bag material has an absorbency determined as follows:

Free Swell Capacity, factor=5.78

Centrifuge Capacity, factor=0.50

Free Capacity (g/g):

$\frac{\begin{matrix}\left\lbrack {{{drip}\mspace{14mu}{{wt}(g)}} - {{dry}{\mspace{11mu}\;}{bag}\mspace{14mu}{{wt}(g)}} -} \right. \\{\left( {{AD}\mspace{14mu}{SAP}\mspace{14mu}{{wt}(g)}} \right\rbrack - \left\lbrack {{dry}{\mspace{11mu}\;}{bag}\mspace{14mu}{{wt}(g)}*5.78} \right\rbrack}\end{matrix}}{\left\lbrack {{AD}\mspace{14mu}{SAP}\mspace{14mu}{{wt}(g)}*Z} \right\rbrack}$

Centrifuge Capacity (g/g):

$\frac{\begin{matrix}\left\lbrack {{{centrifuge}\mspace{14mu}{{wt}(g)}} - {{dry}\mspace{14mu}{bag}\mspace{14mu}{{wt}(g)}} -} \right. \\{\left( {{AD}\mspace{14mu}{SAP}\mspace{14mu}{{wt}(g)}} \right\rbrack - \left\lbrack {{dry}\mspace{14mu}{bag}\mspace{14mu}{{wt}(g)}*0.50} \right\rbrack}\end{matrix}}{\left\lbrack {{AD}\mspace{14mu}{SAP}\mspace{14mu}{{wt}(g)}*Z} \right\rbrack}$Z = Oven  dry  SAP(g)/Air  dry  SAP(g)

Example 8 Method for Determining Absorbency Under Load (AUL)

In this example, a method for determining Absorbency Under Load (AUL) isdescribed.

The materials, procedure, and calculations to determine AUL were asfollows. Reference is made to FIG. 2.

Test Materials:

Mettler Toledo PB 3002 balance and BALANCE-LINK software or othercompatible balance and software. Software set-up: record weight frombalance every 30 sec (this will be a negative number. Software can placeeach value into EXCEL spreadsheet.

Kontes 90 mm ULTRA-WARE filter set up with fritted glass (coarse) filterplate clamped to stand.

2 L glass bottle with outlet tube near bottom of bottle.

Rubber stopper with glass tube through the stopper that fits the bottle(air inlet).

TYGON tubing.

Stainless steel rod/plexiglass plunger assembly (71 mm diameter).

Stainless steel weight with hole drill through to place over plunger(plunger and weight=867 g)

VWR 9.0 cm filter papers (Qualitative 413 catalog number 28310-048) cutdown to 80 mm size.

Double-stick SCOTCH tape.

0.9% Saline.

Test Procedure:

1. Level filter set-up with small level.

2. Adjust filter height or fluid level in bottle so that fritted glassfilter and saline level in bottle are at same height.

3. Make sure that there are no kinks in tubing or air bubbles in tubingor under fritted glass filter plate.

4. Place filter paper into filter and place stainless steel weight ontofilter paper.

5. Wait for 5-10 min while filter paper becomes fully wetted and reachesequilibrium with applied weight.

6. Zero balance.

7. While waiting for filter paper to reach equilibrium prepare plungerwith double stick tape on bottom.

8. Place plunger (with tape) onto separate scale and zero scale.

9. Place plunger into dry test material so that a monolayer of materialis stuck to the bottom by the double stick tape.

10. Weigh the plunger and test material on zeroed scale and recordweight of dry test material (dry material weight 0.15 g+/−0.05 g).

11. Filter paper should be at equilibrium by now, zero scale.

12. Start balance recording software.

13. Remove weight and place plunger and test material into filterassembly.

14. Place weight onto plunger assembly.

15. Wait for test to complete (30 or 60 min)

16. Stop balance recording software.

Calculations:

-   -   A=balance reading (g) * −1 (weight of saline absorbed by test        material)    -   B=dry weight of test material (this can be corrected for        moisture by multiplying the AD weight by solids %).        AUL (g/g)=A/B (g 1% saline/1 g test material)

While the preferred embodiment of the invention has been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention.

1. A method for crosslinking a carboxylated polymer, comprising (a)treating a carboxylated polymer having a plurality of carboxyl groupswith a triazine crosslinking activator in an aqueous solvent to providean activated carboxylated polymer; (b) reacting the activatedcarboxylated polymer in an aqueous solvent with an amine compound havingat least one amino group reactive toward an activated carboxyl group ofthe activated carboxylated polymer to form a plurality of amide bonds toprovide a crosslinked carboxylated polymer.
 2. The method of claim 1,wherein the carboxylated polymer is a carboxyalkyl cellulose.
 3. Themethod of claim 1, wherein the carboxylated polymer is a carboxymethylcellulose or a carboxyethyl cellulose.
 4. The method of claim 1, whereinthe carboxylated polymer is selected from the group consisting of apolyacrylic acid, a polymaleic acid, a polyaspartic acid, and acopolymer of acrylic acid and acrylamide.
 5. The method of claim 1,wherein the carboxylated polymer is a polyacrylic acid.
 6. The method ofclaim 1, wherein the amine compound is a water-soluble diamine.
 7. Themethod of claim 1, wherein the triazine crosslinking activator is2,4,6-trichloro-1,3,5-triazine.
 8. The method of claim 1, wherein thetriazine crosslinking activator is2-chloro-4,6-dimethoxy-1,3,5-triazine.
 9. The method of claim 1, whereinthe amine compound includes at least one of a primary amino group or asecondary amino group.
 10. The method of claim 1, wherein the aminecompound includes two primary amino groups.
 11. The method of claim 1,wherein the amine compound includes a primary amino group and asecondary amino group.
 12. The method of claim 1, wherein the aminecompound includes two secondary amino groups.
 13. The method of claim 1,wherein the amine compound is a poly(oxyalkylene)diamine.
 14. The methodof claim 1, wherein the crosslinked carboxylated polymer comprisesdiamide crosslinks.
 15. The method of claim 1, wherein the aminecompound includes at least one of a tertiary amino group or a quaternaryamino group.
 16. The method of claim 1, wherein the amine compoundincludes a primary amino group and at least one of a tertiary aminogroup or a quaternary amino group.
 17. The method of claim 1, whereinthe amine compound includes a secondary amino group and at least one ofa tertiary amino group or a quaternary amino group.
 18. The method ofclaim 1, wherein the amine compound is 3- dimethylamino)propylamine. 19.The method of claim 1, wherein the crosslinked carboxylated cellulosecomprises ionic crosslinks.